I. Field of the Invention
The present invention relates generally to a device for use in mobile recreational vehicles, marine vessels, and other such mobile self-contained living environments. The device monitors ga furnace heater operation and cabin environment temperature and if the furnace fails to light automatically cycles the thermostat to retry for furnace ignition.
II. Description of the Prior Art
Typically mobile recreational vehicles (RV's), houseboats, marine vessels, and other such mobile self-contained environments provide for cabin environment heating by a thermostatically controlled furnace which is typically fueled by combusting a portable supply of liquefied petroleum gas (LPG), also known as propane. The furnace is typically powered by an on board battery for electrical demands such as blower or fan operation, opening and closing burner valves, and spark ignition functions. As is known in the art a thermostat mounted in the RV or the like acts like a thermal switch, closing when sensing the ambient temperature has fallen below a desired setpoint temperature. The furnace senses the closed switch through the electrical connections and turns on to provide heat and raise the temperature.
It is known in the art that the battery systems of RV's and the like are typically used for long periods of time, often when an external source of electricity such as from an RV park or dockside are not available. The voltage available from the battery to operate the various appliances may be much lower than that when fully charged. It is also known in the art that the commercially available gas powered furnaces are prone to ignition failure when available voltage is low. Other common scenarios which lead to ignition failure are extremes of cold and/or humidity, and moisture or air in the propane tank or delivery system.
Another common problem relating to the ignition failures of typical RV furnaces also relates to the propane system. The liquified petroleum gas is stored in a liquid form under relatively high pressure in the LPG supply tank. Gas pressure regulators are normally installed at or near the propane tank and regulate the gas pressure in the lines, providing the propane gas at their outlets at a relatively low pressure. The gas pressure regulators often fail to regulate the pressure in the lines within the range suitable for ignition at the furnace. Further, even with a good pressure regulator the gas pressure delivered to the furnace may be low due to excessive flow to other propane fueled appliances simultaneously demanding flow of propane. For example, occupant cooking, water heater turn-on, and absorption refrigerator burner turn-on may all occur simultaneously, increasing the propane gas flow demand and possibly causing a low propane gas pressure to exist downstream of the pressure regulator. In this situation, a low gas pressure supplied to the heating furnace may lead to ignition failure, as well as inoperability of other propane fueled appliances in the RV.
Occupants of the RV have no way of knowing which of these scenarios may be the most significant factor in gas furnace ignition failure.
Normally when such conditions exist and the furnace fails to ignite, the safety functions of the furnace shut off the flow of fuel. However, with most furnaces commercially available and installed in the RV environment the fan or blower motor will continue to operate. Often the occupant will note the ignition failure by the lack of warm air, and cycle or reset the thermostat by shutting it off and turning it back on again, typically after a short delay. The delay allows for the furnace to totally shut down as the blower motor typically continues for a few minutes as a safety feature after the thermostat is off to ensure the combustion chamber is clear of gas. Often after a simple such reset or possibly two the furnace will ignite, due to possible purging of air in the lines through the furnace, or the existence of marginal operating conditions.
As is known in the art, failure of the furnace to ignite has several negative implications if not detected. The furnace blower will continue to run, albeit blowing cold air instead of warm air. Also, it is known that although typical furnaces in RV's and the like draw very little standby current (typically a fraction of an ampere) when not running, a running furnace will draw a relatively large current for blower or fan motor operation. Since the blower is blowing cold air, the ambient temperature inside the RV will not rise as intended but instead actually fall increasingly rapidly since colder outside air is being drawn into the interior and distributed through the ducting system of the RV. Since the ambient temperature inside the RV is not being raised to the desired thermostat setpoint temperature, and in fact moving farther below it, the furnace blower will continue to run indefinitely. Worse, if unattended, the on board battery system will continue to be drained constantly at a very significant rate until completely dead and no appliances can be used. A common scenario for such failures is for the RV occupants to wake up very late in the night or early in the morning in a very cold environment to find the furnace blowing cold air. Often the battery has then been depleted to the point where it cannot supply sufficient voltage for furnace ignition. Another common scenario, particularly in cold climates where the demand for propane by the furnace and water heater appliances is intermittent but relatively high is for an otherwise functional system to become nonfunctional due to the depletion of fuel in the propane tank at some point in the night or during an unattended interval.
There is a need in the art for a system which detects the failure of a typical RV furnace to ignite and cycles or resets the thermostat until ignition occurs, thereby preventing the blowing of cold air and battery depletion. Such a novel device would provide autonomous operation, emulating the presence and attention of the RV occupant whenever the thermostat closes and calls for the furnace to provide heat.
There is a further need in the art for further such autonomous operation such that when the propane tank is emptied of fuel at some point during the cycles of furnace operation the thermostat would be turned off or disabled. Such a novel device would emulate the accurate conclusion of the RV occupant that further repeated attempts at relighting the furnace would be fruitless and counterproductive.
There is a further need in the art for a device providing further such autonomous operation such that the occurrence of any such condition above and beyond emptying of the propane tank which prevents ignition of the furnace would similarly emulate the accurate conclusion of the RV occupant that further repeated attempts at relighting the furnace would be fruitless and counterproductive.
The prior art does not provide for any such system.
There is a further need in the art for such a system which also provides for monitoring of the propane gas pressure delivered to the appliances in the RV to assist in determining the cause for furnace ignition failures. Further, there is a need in the art to provide an indication to the RV occupants when the gas pressure falls below the minimum allowable pressure for appliance operation. Similarly, there is a need in the art for a system which indicates pressures higher than the maximum allowable for appliance operation.
The prior art does not provide for any such system.
Various examples of the prior art exist for thermostat design, but these are not central to the present invention nor its autonomous operation which only interfaces with such various devices as thermostats in an RV and is not concerned with the internal operation or detailed design of same. For example U.S. Pat. No. 3,621,434 of Gerich provides for a detailed mechanism internal to the workings of a trip-free manual reset thermostat but does not address the need in the art discussed herein.
U.S. Pat. No. 4,188,604 of Maybee provides for a regulator for thermostats which at preselected times changes the temperature at which heat is called for by the thermostat. The device and all other similar devices such as electronic implementations commercially available in the recent art do not meet the need in the art to provide autonomous thermostat cycling or resetting features of the nature required to anticipate and correct for furnace ignition failure.
U.S. Pat. No. 3,861,589 of Carlson provides for an electronic thermostat accepting either AC or DC current and provides for a clean circuit opening when the applied circuit voltage is low. These are advantageous in the case of controlling the winding of a solenoid valve to supply gas to a furnace, but does not meet the need in the art for autonomous detection of RV furnace ignition failure due to gas depletion or low voltage or marginal operating conditions.
U.S. Pat. No. 4,338,891 of Blitz controls the temperature in automotive storage compartments integral with the fluid cooled internal transport system of the internal combustion engine of the self-powered vehicle by circulating engine coolant fluid through a heat exchanger. Thus it does not meet the need in the art to address the ignition shortcomings of a gas furnace heating unit controlled by a thermostat in an RV or similar environment, the heating systems of which are independent from the transport engine, if one even exists in the RV (such as for example would not be the case with a towable trailer).
U.S. Pat. No. 4,420,033 of Franz controls the temperature in vehicle passenger compartments through a vacuum operated servoactuator which cycles the cooling refrigerant compressor and modulates the heater core water valve of the vehicle. Thus it also does not meet the need in the art to address the ignition shortcomings of a gas furnace heating unit controlled by a thermostat in an RV or similar environment, the heating systems of which are independent from the cooling refrigerant compressor driven by the transport engine, if one even exists in the RV.
U.S. Pat. No 4,416,324 of Sutch et al, which also controls the temperature in vehicle passenger compartments, regulates a blower speed and air door opening. Thus it also does not meet the need in the art to address the ignition shortcomings of a gas furnace heating unit controlled by a thermostat in an RV or similar environment.
U.S. Pat No. 4,750,671 of Heinle et al provides a regulating device for a heating system of a motor vehicle by regulating air flow so as to balance the air temperatures of driver and passenger sides through throttle valve regulation and so does not meet the need in the art to address the ignition shortcomings of a gas furnace heating unit controlled by a thermostat in an RV or similar environment.
U.S. Pat. No. 4,543,795 of Ward et al provides for regulating the temperature within the cabin of a vehicle such as a truck tractor or an agricultural vehicle with a power circuit which applies electrical power to a heating/cooling device and so does not meet the need in the art to address the ignition shortcomings of a gas furnace heating unit controlled by a thermostat in an RV or similar environment.
U.S. Pat. No. 4,514,976 of Christoff relates to environmental control units for aircraft and the like through an improved integration with the compressor turbomachinery of such vehicles as large passenger planes and so does not meet the need in the art to address the ignition shortcomings of a gas furnace heating unit controlled by a thermostat in an RV or similar environment, the heating systems of which are independent from turbomachinery, which do not exist in an RV.
U.S. Pat. No. 4,308,993 of Buss is also a heating system for aircraft cabins which uses engine bleed air or compressor air for heating the passenger space and so similarly does not meet the need in the art to address the ignition shortcomings of a gas furnace heating unit controlled by a thermostat in an RV or similar environment.
U.S. Pat. Nos. 3,711,044 of Matulich, 3,825,212 of Darges et al, and 3,861,624 of Lear all deal with various such mechanisms for aircraft cabin environment temperature and so similarly do not meet the need in the art to address the ignition shortcomings of a gas furnace heating unit controlled by a thermostat in an RV or similar environment.
U.S. Pat. No. 4,784,214 of Penson et al relates to a secondary remote control system for an RV's air conditioning unit, typically roof mounted and possibly including an auxiliary heating unit. The auxiliary heating unit is a resistive electrical strip and so does not meet the need in the art to address the ignition shortcomings of a gas furnace heating unit controlled by a thermostat in an RV or similar environment.
Although the prior art provides for displaying the level of propane in the supply tank as it exists stored under high pressure in its liquid form, the art does not provide for monitoring the gas pressure in an RV as delivered to the furnace and other appliances, downstream of the pressure regulator. Commercially available dial gages are available and can be utilized for diagnostic purposes on the propane system of an RV, but being a portable tool by nature are designed only for temporary use and can only be read locally at the point of mechanical connection. Nor does the prior art provide for the indication or alarm of too low or too high a gas pressure being supplied to the propane fueled furnace or other appliances of an RV.
It is apparent then that the prior art does not satisfy the need for a system which detects the failure of a typical RV furnace to ignite and cycles or resets the thermostat until ignition occurs, thereby preventing the blowing of cold air and battery depletion. Nor does the prior art satisfy the need for autonomous operation such that when the propane tank is depleted or conditions arise which cause repeated attempts to ignite the furnace to fail the relighting attempts are recognized as fruitless and counterproductive and the thermostat is autonomously disabled. Nor does the prior art satisfy the need for a permanently installed remote monitoring and alarming capability in an RV of the gas pressure as delivered to the furnace to assist in determination of the cause of ignition failure.